I've heard that the diameter of the engines on the Boeing 777 is comparable to the fuselage diamater on a
Boeing 737. Is that true? I know they're big but are they really THAT big?- question from Matt

According to Boeing, the internal cabin diameter of the newer 737
models is 11 ft 7 in (3.53 m). The Rolls Royce Trent 800 series turbofan engines used on the
Boeing 777 have a maximum diameter of 9 ft 2 in (2.8 m). Meanwhile,
Pratt & Whitney states that the fan diameter of its PW4000 series used on the 777 is slightly larger at 9 ft 4 in
(2.85 m). The 737 fuselage is therefore about 2 ft 3 in, or 25%, larger than the 777 engine diameter. As aircraft
engines go, those of the 777 are rather large, but the final judgement depends on your defintion of "comparable."

Massive General Electric turbofan on the Boeing 777-300ER

However, the comparison becomes even more incredible if we consider the new General Electric GE-90-115B turbofans
that will be fitted on the latest long-range 777-200LR and 777-300ER models. This engine is the largest and
most powerful turbofan built to date, being some 11 ft 3 in (3.43 m) in diameter. In this case, the 737 cabin is a
mere 3% wider than the 777 engine.
- answer by Joe Yoon, 30 September 2001